The present invention relates in general to an optical waveguide coupling device and pertains, more particularly, to an optical switch and an associated improved process of manufacturing the optical switch.
An optical switch is shown in copending application Ser. No. 521,512 filed Aug. 8, 1983. Such an optical switch causes light to switch into and out of a waveguide from an input laser beam by changing the intensity of the input laser beam or by changing the intensity of another (control) laser beam. In order to make an optical switch, the material forming the waveguide has to have a large non-linear index of refraction and there also has to be a way of controllably depositing the material to form the waveguide.
FIG. 1A schematically illustrates a traditional waveguide which is formed by three layers of material illustrated as layers 1, 2, and 3. The second layer has a larger index of refraction than either of the first or third layers. Reference is also made to FIG. 1B herein which shows an optical switch, such as in the aforementioned copending application Ser. No. 521,512, including a grating located and etched at the interface between layers 1 and 2. Layer 1 is often air. This grating allows light from an external beam to be coupled into the waveguide.
FIG. 1B shows the input beam 6 along with the transmitted beam 7 and the reflected beam 8. The grating is illustrated at 9. FIG. 1B also illustrates the waveguide intensity profile 10, which, it is noted, extends over all three layers and extends to a zero field only at the outer boundaries.
To form a non-linear optical coupling switch, the material of layer 2 has a large non-linear index of refraction. The index of refraction is given by the following equation: EQU n=n.sub.0 +n.sub.2 I,
where
n.sub.0 =linear index of refraction, PA1 n.sub.2 =nonlinear index of refraction, and PA1 I=laser intensity.
Also, in order that the optical switch be, say, faster than a counterpart electronic version, the non-linearity, preferably, has a relaxation time on the order of or less than 1 psec. One class of materials that satisfies these requirements is the polydiacetylenes, a family of organic polymers. However, the problem has been to deposit a smooth, optically flat, oriented film, such as a film having a thickness of approximately one wavelength, on a low index of refraction substrate. Moreover, with the system of FIG. 1B, idealized switching is not possible because part of the energy in the waveguide mode is in the material of layer 3, and some of the input beam is thus transmitted through the material of layer 3. Also, it is difficult to controllably etch gratings in the polymer.